When using a computer screen in a public location, users necessarily run the risk of having someone else view their documents (by accident or otherwise). This lack of privacy may pose a significant problem to a user if the need to view sensitive and/or private documents arises while the user is in a public location. This is true whether the display screen is under the user's control (e.g., a personal notebook computer or personal digital assistant) or not (e.g., a screen in an Internet cafe or at a vendor/customer site.). This problem is further compounded by the fact that both sensitive and non-sensitive data may appear in the same document. A copy of an online bank statement, for example, may include highly sensitive information (e.g., balances, transactions, etc.) as well as less sensitive information (e.g., name of the bank, the bank's address, date, etc.). Even if the user is only interested in only one particular piece of information (e.g., whether a particular check has cleared), all the information in the bank statement will nonetheless be publicly displayed.
Thus, users currently either avoid accessing sensitive information, if possible, or they accept the risk of having their sensitive documents viewed by others. A number of existing techniques provide minimal protection to the user. For example, notebook screen filters, which severely limit the field of view of the screen, may offer the user some level of protection and privacy. Alternatively, users may have access to liquid crystal display (“LCD”) screens that deliberately have the top polarizer removed, making them appear totally white to anyone who is not wearing glasses with the correct polarization filter angle. Yet another solution may be to segment the display of private and open information into separate screens, web pages, dialog boxes, etc. The author of the document may not, however, know where the document will be read and what the sensitivity of that information is in that environment. Segmentation may therefore be ineffective and/or cumbersome.